Just made my first trip in my 26 tudor since the engine rebuild and conversion back to magneto from a distributor equiped car. When i first pulled out of my driveway i was running on battery with the headlights on low for safety, i soon realized that i should switch to mag. when i did so it ran very good but it killed the headlights, i wasn't sure if going to mag had anything to do with it so i switched the lights to high beam and after a few seconds they blew out also. when i got back to the shop i realized that the fillament in the tailight had also blew.

I'm using 20 watt halogen bulbs that i purchesed from macks.so i have no idea what happened did i buy crap bulbs or is there a short in the switch somewhere,. any thoughts. as i ssy the lights where fine till making the change to mag.

I would check your switch wiring. Could be when you switched to mag you fed the higher voltage from the mag to headlight circuit or your generator output is set too high or when you switched the voltage spiked and fried your bulbs. Unless you are planning a lot of night driving I would just use the normal head light bulbs.

I have blown headlight bulbs when I lost one of the main wires to the battery. This let the generator spike up causing much to high a voltage for the headlight bulbs. Switching to mag should not have caused the problem. I would not blame the bulbs, compare your wiring to one of the wiring diagrams.

Setting the gen. too high would not knock out all the bulbs so quickly unless a battery cable came off. even then they would most likely get real bright and then go out. I would guess something is wired wrong and when Scott switched to mag the headlights also got mag current which could be as high as 20 or more volts.

I think Mark has the answer. The headlights should be fed from the battery even when the engine is running on mag. Only other thing which would do it would be a loose connection between ammeter and battery. That is not likely because you have a starter. It could be loose between starter switch and ignition switch. Be careful how you wire the switch. You don't want any connection between the battery and the magneto or you will discharge the magnets. There should be a small wire between the ammeter and the ignition switch That wire should be on the battery terminal of the switch. If it is on the mag terminal, that's your problem. Norm

As I understand it, whether the ignition is running on BAT or MAG should have no effect on the lights. While the car is running on MAG the lights are still running off the battery, and the generator is still keeping it charged. I'm with those who suspect a wrong connection somewhere. Check your wiring and connections with the diagram. The generator should be set so the ammeter shows a slight charge of just an amp or two when the lights are on.

Nathan look at the switch in the diagram above. The dashed arrows show that the current goes from BAT (K) to DIM (O) and BRIGHT (L). The lights operate only off the battery. Note the dashed arrow from MAG (Z) goes only to the coil box (X), not to the lights. This is the system used in the "electric" cars (1919-1927). It's the 1915-1918 cars that run the lights on magneto power. Here's the diagram for that.

Note that the wire from the mag post goes to a terminal on the coil box, and another wire goes from there to the light switch.

Gentlemen, thank you for taking the time to reply. last night i replaced the headlight wiring harness and distribution block, i also pulled the switch and carefully checked all of my wiring against the schematic for the 26/27 cars and everything is in order. i checked the voltage output at the generator while running and it's showing 8 volts without the lights on. not sure what it is with the lights on, i forgot, brain fart. but i also checked the output at the headlight pigtails and it didn't matter if the car is running either on battery or mag but i'm getting a wild and fast fluctuation on my multi meters, ranging from 2 to 20 volts, i tried both AC and DC scales and same thing.

So now i'm back to thinking the switch is shorting out and picking up current from the red mag wire. is this possible? any thoughts?

Just got back home and figured a quick check with the ohm meter should let me know whats going on, and sure enough there's continuity between the high and low headlight lugs and mag lug on the back of the switch. luckily nothing between mag and power.

Not sure how common this problem is but i just thought i'd let everyone know what i found.

If you are using a digital meter Scott you will see strange readings. Find an old analog meter with a needle to troubleshoot Model T's.

Be careful using schematics even from reputable sources as they may contain wiring mistakes. Even in recent times a dealer had some diagrams with timer wiring errors. The 1919-27 wiring diagram above is correct although a bit hard to read with older eyes.

Are you using a digital meter by any chance? If yes then ignore ALL readings and start over. The ignition on a Model T ford puts out heavy interference that will screw up your readings. It has nothing to do with the quality of the meter. I have laboratory grade Fluke Digital meters and they work the same. When the engine is totally stopped and no coil is buzzing then you can read with your digital meter.

If you were using analog meter and measured 8V at the generator then I would assume the engine was idling at that time. That voltage would go way up when you speed up the motor and that would blow your bulbs. The high and low lugs would show continuity to ground as would your magneto lug so that is normal. If you measured between the mag and the headlight wires when bulbs are inserted in the socket then you are measuring continuity to ground through the light bulb filaments (very low resistance when not lit) and then the magneto coil is a very low resistance to ground as well (less than 1/4 ohm) so your readings of mag to bright and/or dim lugs should indeed show continuity and that is not likely coming from the switch unless you are sure you can measure the difference in resistance between zero ohms and perhaps 1 or 2 ohms. They both look about the same.

I am betting it is that you used the Ford manual to set up your charging and have set the generator way way too high. It is easy to do and you need to address it quickly or you may damage your generator.

John, thank you, i was using a digital meter. never gave a thought about the headlights completing a path to ground and providing continuity, the funny thing is the tailight circuit wont show continuity when i probe between that lug and the mag lug?

But it sounds like i need to address my charging rate. so far the battery is staying at 6.5 volts but the ammeter is showing a 10 amp charge rate at idle, not sure what it is going down the road.

Your existing ammeter will be showing you anything but the exact charge rate Scott. There are a few items you should invest in before your generator dies unnecessarily, such as a voltage regulator and a precision ammeter which can be bought from funprojects. That little investment will save you a lot of headaches and dollars in the long run. The funprojects regulator comes with full instructions on how to adjust the generator and you can even download the instructions directly from the website without having to buy anything to familiarize yourself with the product.

Thanks for all the help guys, Garnet i do recall seeing the voltage regulators in the macs catalog, i'll check out Johns site and order one up. Steve that'll be the next book i buy. John i owe you a big thanks for saving me from buying a new ignition switch that i didn't need.

To correctly set up the generator, do get one of John's ammeters but hook it up in paralleled to the one in the dash. Set the third brush IAW the Fun Projects meter. If you purchase the Fun Projects VR, follow the instructions exactly, to include verifying the adjustment the next day. Using the FP meter as the rule, you can see what the in dash meter is indicating and note the reading of the dash versus the actual on the FP meter for future reference. I'd hold onto the good FP meter for future use.

I put the stock bulbs back in and have driven about 40 miles since, and there fine. not sure what my generator is putting out as i only have a digital gauge and not an analog, but the battery shows 6.37 to 6.51 every time i check it while parked and not running. i really think it was the chinese halogen bulbs.

I think that with the extra juice the Halogen bulb may have been pulling and running the coils on battery that there could have been an output spike from the generator when you took the coils out of the circuit and switched to magneto. But then electrical things are a mystery to me and I try to keep the smoke in.